1. Field of the Invention
This invention relates to a disc driving apparatus for rotationally driving a sheet-like magnetic disc for recording and/or reproducing information signals on or from the magnetic disc. More particularly, it relates to a disc driving apparatus in which, for protecting the magnetic disc, the contact between the magnetic head and the magnetic disc is controlled in connection with the operation of loading the disc cartridge accommodating the magnetic disc.
2. Brief Description of the Related Art
Up to now, as a recording medium for recording information signals, such as data signals, a magnetic disc comprising of a base member in the form of a disc-shaped thin film sheet, and a magnetic layer deposited thereon as a signal recording layer, has been used extensively. This type of magnetic disc, however, may be damaged easily during handling since the brittle thin film sheet is used as the base member. In addition, the slightest injury to the magnetic layer results in signal dropout because of the elevated recording density of the magnetic disc.
For this reason, this type of the magnetic disc is accommodated in main cartridge body and loaded in this state into the recording/reproducing apparatus.
The disc cartridge comprising the magnetic disc accommodated in the main cartridge body is shown for example in FIGS. 1 and 2.
The disc cartridge 1 comprises a main cartridge body 2 consisting of an upper half 2a and a lower half 2b, each in the form of a rectangular flat plate, abutted and connected to each other, and a sheet-like magnetic disc 3 in the form of a disc which is rotatably accommodated in the main cartridge body 2. A central disc-shaped member 4 formed by a metal plate and operating as a mounting means to a disc table of a disc driving device of a magnetic recording and/or reproducing apparatus into which the disc cartridge is loaded, is provided at the center of the magnetic disc 3 accommodated in the main cartridge body 2. Referring to FIG. 2, the central disc-shaped member 4 has a central opening 5 engaged by a central driving shaft of the disc table, and a rectangular opening 6, at a position offset from the center of the member 4, engaged by a driving pin of the disc table. When the disc 3 is received within the main cartridge body 2, the disc-shaped member 4 is loosely fitted in a disc table inserting opening or aperture 7 formed at the center of the lower half 2b of the main cartridge body 2 so as to be exposed to the outside of the main cartridge body 2. In the upper and lower halves 2a, 2b of the main cartridge body 2 are formed head inserting openings 8a, 8b by which the signal recording surface of the magnetic disc 3 is exposed to the outside along the disc radius and by means of which the magnetic head of the recording/reproducing apparatus is inserted into the disc cartridge. These head inserting openings 8a, 8b may be closed and opened by a shutter 9 slidably mounted on the main cartridge body 2. This shutter 9 is formed by bending a thin metal plate into a sectional shape of a letter U and is slidably mounted on the upper and lower major surfaces of the main cartridge body 2 from the front side of the main cartridge body 2. The shutter 9 is also formed with openings 10, 10 which register with the head inserting openings 8a, 8b on sliding movement of the shutter 9 to open the head inserting openings 8a, 8b. The shutter 9 is usually biased by a spring, not shown, to a position of closing the head inserting openings 8a, 8b in which the openings 10 do not register with the head inserting openings 8a, 8b.
The recording/reproducing apparatus for a disc employing this type of the disc cartridge 1 as the recording medium is disclosed in, for example, U.S. Pat. No. 4,750,065.
The disc drive device disclosed in the U.S. Patent includes a disc table on which is loaded magnetic disc 3 accommodated in the disc cartridge 1, a disc rotating-driving device for rotationally driving the magnetic disc 3 by rotation of the disc table and a cartridge holder supported for vertical movement along the axis of rotation of the disc rotating-driving device and moved towards the disc table in association with the inserting operation of the disc cartridge 1. This cartridge holder is provided with a shutter opening and closing mechanism for opening and closing the shutter 9 depending upon the loading and unloading operation of the disc cartridge 1.
The recording and/or reproducing apparatus is also provided with a magnetic head device which is moved in association with the operation of insertion of the disc cartridge 1 into the cartridge holder for bringing the magnetic head into contact with the magnetic disc 3 via head insertion openings 8a, 8b of the disc cartridge 1. This magnetic head device is provided with a head shifting unit for shifting the magnetic head along the radius of the magnetic disc 3 with the magnetic head kept in contact with the disc 3.
With the above described recording and/or reproducing apparatus for a disc, when the disc cartridge 1 is inserted into the cartridge holder, the shutter 9 is moved by the shutter opening and closing mechanism provided in the cartridge holder to open the head inserting openings 8a, 8b. When the disc cartridge 1 is inserted and loaded in the cartridge holder, the cartridge holder is lowered towards the disc table of the disc rotating-driving device. The magnetic disc 3 within the disc cartridge 1 is loaded on the disc table by means of the central disc-shaped member 4. The magnetic head is also moved to follow the descent of the cartridge holder towards the disc table into contact with the magnetic disc loaded on the disc table. With the magnetic head in contact with the magnetic disc, the disc table is driven into rotation for recording/reproducing information signals on of from the magnetic disc by means of the magnetic head.
With the above described disc cartridge in which the magnetic disc 3 is accommodated in the main cartridge body 2 and the head inserting openings 8a, 8b in the main cartridge body 2 are closed by the shutter 9, it is possible to prevent the signal recording surface of the magnetic disc from being contaminated by inadvertent contact of the finger of hand with the magnetic disc during non-use time, such as during storage, of the magnetic disc.
However, with the above disc cartridge 1, since the central disc-shaped member 4 of the magnetic disc is loosely fitted in the disc table inserting aperture 7 formed in the lower half 2b so as to be exposed towards the exterior of the main cartridge body 2, a small gap is formed between the central disc-shaped member 4 and the disc table inserting aperture 7, such that minute dust and dirt are introduced into the inside of the main cartridge body 2 by way of this small gap. There is also the risk that dust and dirt may be introduced into the main cartridge body 2 by means of the head inserting openings 8a, 8b which are opened when the shutter 9 is actuated in association with the loading of unloading of the disc cartridge 1 into and out of the recording and/or reproducing apparatus.
When the dust and dirt are introduced into the inside of the main cartridge body 1 so as to be affixed on the signal recording surface of the disc 3, such dust and dirt are interposed between the magnetic head and the disc 3 when the magnetic head is contacted with the disc. Above all, with the above described conventional recording and/or reproducing apparatus for a disc, since the disc 3 is set into rotation after the disc 3 is loaded on the disc table and the magnetic head is contacted with the disc, there is the risk that the rotation of the magnetic disc be started with the dust and dirt interposed between the magnetic head and the disc 3.
When the magnetic disc is rotated with the dust and dirt interposed between the magnetic head and the magnetic disc 3, the disc or the head may be damaged easily by such dust and dirt. The result is that not only the satisfactory recording/reproducing characteristics cannot be maintained but the magnetic head and/or the magnetic disc may become unusable.